Vision begins with the absorption of photons by the visual pigments - rhodopsin. It is generally believed that light causes an isomerization of the chromophore and thereby initiates a chain of events, known as the intermediate steps of phototransduction, which finally leads to a conductance change of the photoreceptor cell membrane. Several lines of evidence suggest that biochemical reactions are involved in these processes although the exact mechanisms are not yet identified. Among the many Drosophila visual mutants isolated so far, several appear to have defects in the intermediate steps of phototransduction. In our laboratory, we are studying photoreceptors of these mutants with various techniques of electrophysiology, biochemistry, genetics and immunology. We hope to identify certain photoreceptor proteins which are likely to be associated with the fundamental mechanisms of phototransduction. We will then raise monoclonal antibodies against these proteins. With these and other tools, we could map the structural genes of these proteins and then systematically alter the structure of these proteins through mutations. By observing the physiological effects of these genetic and biochemical manipulations on the photoreceptors, we expect to gain important insights into the molecular mechanisms involved in phototransduction. Since it is likely that the underlying mechanisms of phototransduction are the same for all photoreceptors, including those in our own eyes, it is hoped that our studies on this model system will yield information which not only advances the forefronts of basic knowledge, but could also be useful in understanding and preventing diseases of human eyes.